A long term evolution (Long Term Evolution, LTE) system has two types of frame structures, wherein frame structure type 1 (Type 1) is applicable to frequency division full duplex (Frequency Division Duplex, FDD) and frequency division half duplex. Each wireless frame has a length of 10 ms and consists of 20 time slots, and each time slot is 0.5 ms and is numbered from 0 to 19. FIG. 1 is a frame structural schematic diagram of an FDD mode, and as shown in FIG. 1, one subframe consists of two continuous time slots, for example, subframe i consists of two continuous slots 2i and 2i+1.
Frame structure type 2 (Type 2) is applicable to time division duplex (TDD, Time Division Duplex). FIG. 2 is a frame structural schematic diagram of a TDD mode, and as shown in FIG. 2, one wireless frame has a length of 10 ms and consists of two half frames with a length of 5 ms. One half frame consists of five subframes with a length of 1 ms. A subframe is divided into a normal subframe and a special subframe, wherein the special subframe consists of a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS), and the total length is 1 ms. Each subframe i consists of two time slots 2i and 2i+1 with a length of 0.5 ms.
In a long term evolution system and an LTE-Advance system, downlink control signalling (Downlink Control Information, DCI) contains DL Grant information relevant to downlink transmission which is required to be known by a terminal and UL Grant information relevant to uplink transmission which is required to be known by a UE, etc., and these physical layer control signalling is transmitted on a physical layer control channel (PDCCH), wherein DCI formats (DCI format) are divided into the following types: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 2B, DCI format 2C, DCI format 3 and DCI format 3A, etc., and DCI format size increases with the increase of system bandwidth.
In release (hereinafter “R”) 8/9 of an LTE system and R10 of an LTE-Advance system, a physical layer control channel (Physical Downlink Control channel, PDCCH) for transmitting physical layer control signalling is usually configured on first N OFDM (orthogonal Frequency Division Multiplexing) symbols for transmitting, and the N symbols are usually called as a control signalling transmission area. Hereby in order to distinguish from a newly-added control signalling transmission area of a new release, a control signalling transmission area of R8/9/10 is called as a first control signalling transmission area in the present invention.
Available transmission resources of the first control signalling transmission area are divided into multiple CCE resource elements, and resources occupied by control information are allocated in the unit of CCE, and the resource element CCE herein also can be further divided into multiple REGs; one CCE consists of multiple discontinuous REGs, and usually one CCE consists of 9 REGs, and further, each REG consists of 4 basic resource elements, wherein one basic resource element bears one modulation symbol, and when QPSK modulation is sampled, one CCE can bear 72 bits.
One PDCCH has four aggregation levels, and the four aggregation levels respectively correspond to one PDCCH occupying 1, 2, 4 or 8 CCEs, being called as aggregation level 1, aggregation level 2, aggregation level 4 and aggregation level 8, also correspond to four formats of the PDCCH, that is to say, aggregation level represents physical resource size occupied by physical downlink control channel. Each aggregation level corresponds to g candidate sets, i.e. g positions which can transmit the PDCCH. A UE would blindly detect said four aggregation levels on a candidate set position corresponding to each aggregation level of the first control signalling transmission area so as to determine whether the PDCCH is transmitted, thereby acquiring corresponding downlink control information.
In a release after R10, in order to improve the transmission capacity of a control channel and support control signalling of more users, a new control channel area is considered to be established, and control signalling transmission resources of the same UE can be continuous time frequency resources so as to support a closed-loop precoding technology and improve transmission performance of control information.
Control signalling areas of new and old releases are as shown in FIG. 3, and control signalling of the new release divides part of transmission resources in a PDSCH transmission area of original R8/9/10 for using same in a second control signalling transmission area so as to support the closed-loop precoding technology when the control signalling is transmitted and improve the capacity of control signalling to support control signalling of more users.
Here in the second control signalling transmission area, a dedicated demodulation pilot (DMRS) in R10 can be reused to demodulate control signalling and better support precoding technology. In addition, the second control signalling transmission area is in the unit of RB and can better perform interference coordination.
At the same time, in the light of transmission robustness and no channel information, in the second control signalling transmission area, DMRS also can support open-loop diversity technology, such as SFBC technology or open-loop precoding technology.
In order to better understand the background of the present invention, the following gives some simple introduction about the resource definition of LTE-A: one resource element (RE) of an LTE is one sub-carrier on one OFDM symbol, and a downlink physical resource block (Resource Block, RB) consists of continuous 12 sub-carriers and continuous 14 (12 when an extended cyclic prefix is used) OFDM symbols, and is 180 kHz on a frequency domain and has a time length of a normal time slot on a time domain, i.e. 1 ms, as shown in FIG. 4 (a 5M system).
In order to transmit downlink control information in the second control signalling transmission area, the CCE is likewise required to be redefined, i.e. eCCE; several opinions about the definition of the size of the CCE are as follows: one is to still keep the definition of R8, i.e. 36 resource elements, and another one is 1/n of resource elements being contained in 1 physical resource block.
Problems existed in the conventional art are: the size of the second control signalling area is restricted by the size of a first control signalling area, and other signals, such as CRS, PSS/SSS, PBCH, PRS, CSI-RS, DM-RS and PRS may be transmitted in the second control signalling area, which will result in the decrease of the amount of valid bits of the downlink control information which may actually transmitted in the eCCE, thereby resulting in the increase of valid code rate of an ePDCCH, even the code rate exceeding 1, causing the downlink control information not decoding correctly; therefore, if a UE still performs blind detection fixedly according to four aggregation levels defined in an LTE system, a large amount of blind detection waste may exist, and the expanding of searching space is restricted, and scheduling blocking rate of the downlink control information is increased.